Synthesis, magnetic properties and theoretical calculations of novel nitronyl nitroxide and imino nitroxide diradicals grafted on terpyridine moiety

The synthetic route based on Stille coupling between tributyltinpyridyl derivatives and bromo substituted mono- and dipyridylcarbaldehyde is used for the synthesis of 5,5"-diformyl-2,2':6',2"-terpyridine (8). A sequence of Ullman coupling with 2,3-bis(hydroxylamino)-2,3-dimetbylbutane followed by oxidation under phase transfer conditions affords either 5,5"-Bis(1-oxyl-3-oxo-4,4,5,5-tetramethylimidazolidin-2-yl)2,2':6',2"-terpyridine (10) (diNN-Terpy) or the related 5,5"-Bis(1-oxyl-4,4,5,5-tetramethytimidazolidin-2-yl)2,2':6',2"-terpyridine (11) (diIN-Terpy), where both biradicals display clear intramolecular ferromagnetic interaction between the single spin units as evidenced by ESR spectroscopy. Quantum chemical calculations (ROHF/AM1) are performed showing the triplet ground-state for both 10 and 11 radicals. (C) 2003 Elsevier Science Ltd. All rights reserved